1. Field of the Invention
The present invention relates to torque sensors and more specifically to a type torque sensor which can detect the torque applied to a rotating body or the like, without direction connection or contact therewith and which type of sensor makes use of the so called magnetostriction phenomenon.
2. Description of the Prior Art
JP-A-61-127952 and JP-A-61-127953 disclose previously proposed torque sensors of the type which are front of contact with the rotating body in which the torque is being measured. In these prior art arrangements one or more sensor elements are disposed about the rotating body in a transmission case and secured to ribs flanges or the like of the casing by way of screws or the like.
These sensor arrangements are arranged to project from their mounting sites and juxtapose the peripheral outer surface of the shaft in which torque is to be sensed and to include U shape cores on which exciting and measuring coils are wound.
However, these devices have suffered from the drawback that as they are exposed to only a portion of the rotating shafts they tend to be subject to "eccentricity" noise which is generated when the shaft is subject to the application of torque which induces twisting deformation and causes the portion of the shaft to which the sensor is exposed to become momentarily eccentric.
A further drawback comes in that the voltage output signal of the device is relatively low. To overcome this is necessary to increase the number of windings on the sensing and exciting coils. However, this measure results in the size of the sensor being unacceptably increased to the point wherein disposal in the confines of a transmission case becomes very difficult.
Yet another drawback has come in that the arrangements disclosed in the above mentioned documents have made made use of an amorphous permeable membrane in the form of a ribbon having a thickness of about 20-30 .mu.m and which is fixed by way of a heat resistant bond to the peripheral surface of the shaft in a manner to juxtapose the U shaped cores.
This construction while being intended to facilitate the production of the sensor arrangement has incurred the drawback that there is a difference in the coefficient of expansion of the membrane and the shaft on which the membrane is disposed. Accordingly, when the temperature of the shaft changes the temperature characteristics of the device are impaired in manner which leads to a notable reduction in the accuracy of the sensor unless extreme care and pains are taken when bonding the membrane in place. Accordingly, this provision has in fact had the effect of increasing the number of operations necessary to secure the membrane in place and has notably reduced the productivity of the device.